The present invention relates generally to an injection molding process and more particularly to a method for evaluating moldability characteristics of a plastic resin in an injection molding process.
An injection molding process is one of the most common ways of producing parts and products from plastic resin pellets. In an injection molding process the plastic resin pellets are changed into a viscous material and forced under pressure into a mold of a desired shape. The viscous material is then held under pressure in the mold until it solidifies. Afterwards, the mold is opened and the molded object is ejected. During the injection molding process several variables are measured. The variables are responses to the plastic resin and the injection molding process. In an injection molding process there may be than sixty process response variables that are measured by taking various sensor readings during the process. After the injection molding process has ended, sometimes several quality characteristics are measured on each part in order to determine if the part meets product requirements. The quality characteristics are dependent upon the process response variables. However, the relationship between the process response variables and the quality characteristics for a given resin in an injection molding process is very complicated because of the many variables involved in the process.
Before a new grade of a plastic resin material can be introduced in an injection molding process it is necessary to develop an understanding on the relationship between the process response variables and the quality characteristics. Currently, the only way to determine if a plastic resin can be used in an injection molding process is by physically producing a product in an injection molding process and determining whether the molded product meets the product requirements. If the product does not meet the requirements, then the plastic has to be molded again under different operating conditions. This process continues until the plastic can mold a product that meets specified requirements. This trial and error approach is very time consuming and costly. If one was able to develop a model describing the relationship between the process response variables and the quality characteristics, then a designer would be able to determine how well a new grade of plastic resin could be molded and under what conditions would the resin be able to produce a product that meets the specification requirements. Therefore, there is a need to be able to develop a model describing the relationship between the process response variables and the quality characteristics for a particular plastic resin in an injection molding process so that the model can be used to evaluate whether a new grade of plastic resin can be used to produce a product built to specification requirements.